- A complete meta-analysis of every published study that examined Spotted Owl (Strix occidentalis) responses to wildfire was recently published. Contrary to current perceptions and recovery activities, mixed-severity forest fire does not appear to be a serious threat to owl populations. On the contrary, wildfire was found to create more benefits than costs for Spotted Owls.
In the 1980s, the Spotted Owl became a symbol of the extraordinary biodiversity found in old-growth forests. When the northern subspecies of Spotted Owl was listed as threatened in 1990 under the federal Endangered Species Act (ESA), about 90% of America’s old-growth forest had already been lost to logging. The listing of the Northern and Mexican Spotted Owl drew national attention to the dramatic decline of old-growth forest ecosystems that had been damaged by 50 years of unsustainable logging practices, and forced policy changes in our National Forests’ management. New regulations included: fewer clear-cuts, less cutting of trees over 30 inches in diameter, and fewer cuts that opened up too much of the forest canopy.
Thirty-eight years later, Northern and Mexican Spotted Owls remain listed as threatened with extinction, and the California Spotted Owl is under review for ESA listing. For decades, managing our public forests included designating old growth reserves and critical Spotted Owl habitat where logging was restricted within half a mile of a Spotted Owl nest. In spite of these protections, all three subspecies have continued population declines on forest lands outside national parks, most likely due to fire suppression and continued logging in the owls’ larger year-round home ranges outside the protected nesting core areas.
Because Spotted Owls are associated with dense, old-growth forests, it has often been assumed that forest fires that burn at high severity are similar to clear-cut logging and have a negative effect on Spotted Owl population viability. It has become widely believed among wildlife management professionals that severe wildfire is a contributing cause of recent Spotted Owl population declines, and many land managers believe that forest fires currently pose the greatest risk to owl habitat and are a primary threat to population viability. These beliefs result in fuels-reduction logging projects in Spotted Owl habitat which the USDA Forest Service and US Fish and Wildlife Service insist are actions consistent with Spotted Owl recovery. Those fuels-thinning logging projects are known to harm Spotted Owls by reducing canopy cover and cutting large trees, but the Forest Service and Fish and Wildlife Service claim the risks to the owl from wildfire justifies the harm caused by additional logging.
A systematic review and meta-analysis recently summarized all available scientific research on the effects of wildfires on Spotted Owl ecology and found Spotted Owls are usually not significantly affected by forest fire. Wildfire did not appear to be a serious threat to owl populations, rather wildfire had more benefits than costs for Spotted Owls. The study, published this week in the Ecological Society of America’s journal Ecosphere, suggested that planning and policy documents claiming that forest fires damage or degrade Spotted Owl habitat and seriously threaten population viability are outdated and not scientifically sound. Therefore, fuel-reduction logging intended to reduce fire severity in Spotted Owl habitat will unnecessary harm the owl.
Derek E. Lee, Associate Research Professor at Pennsylvania State University and author of the meta-analysis said, ”This result of no big negative effects of fire on Spotted Owls was not a surprise to me as this species has been living with forest fire for thousands of years. But, it was fascinating to see the positive effects of wildfire on the owls. The positive effects of forest fires on Spotted Owls indicate mixed-severity fires, including so-called mega-fires, such as have been receiving lots of media attention lately, are within the natural range of variability for these forests. The fact that Spotted Owls have adapted to these types of fires over evolutionary time tells us that they have seen this before and learned to take advantage of it.”
The systematic review of effects from the primary scientific literature indicated Spotted Owls are usually not affected by mixed-severity fire as 83% of all studies and 60% of all effects found no significant impact of fire on owl parameters. Meta-analysis of average effects found no significant effects of fire on owls, except for a positive effect on foraging habitat selection for low-severity burned forest. Meta-regression indicated significant positive effects in recruitment, reproduction, and foraging habitat selection for low- and moderate-severity burned forest. Meta-regression also found a significant negative effect of time since fire on breeding site occupancy probability.
Western forest fires typically burn as mixed-severity fires with each fire resulting in a mosaic of different vegetation burn severities, including substantial patches of high-severity fire (5% to 70% of the burned area typically burns at high severity). High-severity fire kills most or all of the dominant vegetation in a stand and creates extremely biodiverse ‘snag forests,’ where standing dead trees, fallen logs, shrubs, tree seedlings, and herbaceous plants comprise the structure. Post-fire vegetation processes then proceed according to the pre-fire vegetation, local wildfire processes, seeds from outside the disturbance, and the conditions at the site.
Spotted Owls occur in western U.S. forests and have been intensively studied since the 1970s. The species is strongly associated with mature and old-growth conifer and mixed-conifer–hardwood forests with thick overhead canopy and many large live and dead trees and fallen logs. Its association with older forests has made the Spotted Owl an important species for public lands management aimed at preserving the last of our old growth forests. Research on Spotted Owls in fire-affected landscapes did not begin until the early 2000s. Much of what scientists previously understood about habitat associations of Spotted Owls was derived from studies in forests that had generally not experienced recent fire, and where ‘non-suitable’ vegetation was a result of logging.
The meta-analysis results represent Spotted Owl responses to mixed-severity wildfires that burned within the past 30 years with representative proportions of high-severity fire in a landscape mosaic. The fires and their effects were representative of wildfires as they burned through current forest structure, fire regime, and climate conditions. Several studies have reported that fires during the past few decades have been larger and more severe than the historical average, while others have disputed this point. Regardless of what is correct about trends in fire severity, Spotted Owls appear fairly resistant and/or resilient to negative effects from recent hot, large fires. This is corroborated by the meta-regressions that explicitly quantified the relationship between amount of high-severity fire and Spotted Owl parameters, and found only a positive significant correlation with reproduction. The finding of no significant negative relationships between amount of high-severity fire and Spotted Owl parameters demonstrates that large high-severity fire patches, including territories that burn 100% at high severity as was seen in sites within several of the studies in this review, do not have unequivocally negative outcomes for Spotted Owls.
Contrary to current perceptions, recovery efforts, and forest management projects for the Spotted Owl, mixed-severity fire as it has been burning in recent decades does not appear to be an immediate, dire threat to owl populations that requires landscape-level fuel-reduction treatments to mitigate fire severity. Empirical studies reviewed demonstrated that wildfires generally have no significant effect, but effects can include improved foraging habitat, reduced site occupancy, and improved demographic rates. Most territories occupied by reproductive Spotted Owl pairs that burn remain occupied and reproductive at the same rates as sites that did not experience recent fire, regardless of the amount of high-severity fire in core nesting and roosting areas.
To further place the results into perspective, mixed-severity fire typically affects a very small portion (0.02%–0.50%) of Spotted Owl nesting and roosting habitat per year. Breeding sites that experienced a typical mixed-severity burn mosaic can be expected to have occupancy probability reduced by -0.06 on average. A 0.06 decline in occupancy is less than typical annual declines in occupancy rates observed in the Sierra Nevada in the absence of large fires. In comparison, post-fire salvage logging causes a mean occupancy probability reduction of -0.18.
Forest fire does not appear to be a serious threat to owl populations, and seemingly imparts more benefits than costs for Spotted Owls, therefore fuel-reduction treatments intended to mitigate fire severity in Spotted Owl habitat are unnecessary. These findings should inform revisions to planning documents to consider burned forest, including large patches of high-severity burned forest, as useful habitat that imparts significant benefits to Spotted Owls.